A transmission device for converting a torque is classified into a rack and pinion for converting a rotational motion to a linear motion or vice versa, and a gear train for converting a rotational speed and a torque while transmitting a rotational motion only. In most cases, a power transmission system of a transmission device for converting a torque mainly adopts a tooth profile according to an involute curve principle. However, a tooth profile according to a cycloid curve principle is used in rare cases.
Such a transmission device for converting a torque is widely used for a variety of industrial machines including semiconductor devices and flat display devices such as liquid crystal display (LCD), plasma display panel (PDP), organic light-emitting display (OLED), etc. In a transmission device for converting a torque that is applied to various industrial machines or is being prepared for application thereto, the transmission device is mostly operated as one pinion is gear-engaged with one rack, and desired power is transmitted as the pinion moves with respect to the rack or the rack moves with respect to the pinion.
However, contrary to the above typical case, when there is a limit in the size of a rack while nominal load capacity is large, a plurality of pinions or pinch gears and driving devices according thereto are required with respect to one rack. In this regard, it is difficult to match synchronization speeds of driving devices. In addition, since embodiment of a deceleration rate appropriate for high speed transmission is difficult, the application of the transmission device for converting a torque is practically delayed and thus improvement of the structure thereof is demanded.